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Downloaded from http://trned.lyellcollection.org/ at Nanyang Technological University on April 26, 2015 278 EDINBURGH GEOLOGICAL SOCIETY. southerly, so that different members of the series are brought in turn against the Skiddaw Slates. This appears to be due to a north and south fault running along this line, and having a downthrow to the west. As regards the origin of the depression in which Derwent­ water is situated, there can be no doubt but that it is to be ascribed to the agency of the ordinary denuding forces, and especially to the action of glaciers, unmistakable traces of which are universally visible. No one, however, who studies the region can doubt that the denuding forces have been directed and powerfully assisted by the peculiarities in the physical geo­ logy of the district. The greater part of the lake has been scooped out of the soft Skiddaw Slates, the resisting Green Slates and Porphyries simply fringing a portion of one side. As I have shown, this difference in the structure of the two sides of the lake is due to the existence of powerful faults. In so far, there­ fore, as this difference in structure has enabled the powers of the denuding agents to be more efficiently applied, and in so far as their course has been determined by this difference, in so far are we justified in asserting that the origin of the valley may be ascribed to the existence of faults as one cause. No one, as far as I am aware, believes that valleys are ever the result of open fissures produced by faulting, though a misconception to this effect is apparently held by some. On the contrary, it is simply held that faults constitute lines of weakness, along which denuding agencies meet with less resistance than elsewhere; and the line of weakness is not caused by the existence of an open fissure, but is due to the apposition of strata of unequal hardness, con­ sequent on the displacement, and also to the inevitable breakage and comminution of the rocks which must occur along every line of dislocation. In this sense, I think, it will be very diffi­ cult to show that faults are not in many cases connected with the formation of valleys in mountainous countries; at the same time that there are, doubtless, many valleys in which no displace­ ment of the strata has occurred. II. Notes on the Geology of Southerness, Kirkcudbrightshire. By WILLIAM JOLLY. (Abstract.) Parallel to the Silurian and Old Eed Sandstone belts of Scot­ land, and running from north-east to south-west, stretches a narrow stripe of Carboniferous strata from the head waters of the Liddel, at the junction of the Cheviots and the Lowthers, to Locher Moss, in the south of Dumfriesshire. This line of the. Coal Measures disappears under the Solway at the mouth of the Downloaded from http://trned.lyellcollection.org/ at Nanyang Technological University on April 26, 2015 ON THE GEOLOGY OF SOUTHERNESS. 279 Nith, forming there the extended Blackshaw Bank, but reappears at two points in Galloway, in the same line of strike. On,e of these is at Southerness, and forms a rough triangle, of which the Ness is the apex, a narrow patch of but a few miles in extent, but rich in fossils and geological points of interest. The other is at Abbey Head, east of Kirkcudbright Bay. These two little patches of the Coal-Measures seem at first sight strange and isolated, as lying apart in the wide Silurian district of Galloway; but their strangeness and isolation at once disappear when they are seen to form part of a Carboniferous belt that stretches from the Northumberland coal-field to Abbey Head in Kirkcud­ bright ; a belt, the counter part and parallel of a smaller patched belt stretching from Girvan to Dunbar on the north; and in­ teresting, moreover, as remnants of the great Carboniferous sheet that probably once covered the wide Silurian uplands of the south of Scotland. The Carboniferous belt just spoken of is, according to the new geological map of Murchison and Geikie, the Carboniferous Limestone series, which lies above the Lower Carboniferous or Calciferous Sandstones, and below the millstone grit and True Coal-Measures. Along this shore the Carboniferous Limestone series is repre­ sented by different limestones, shell, coral, and encrinital sand­ stones, shales, and seams of coal and ironstone, variously intermingled, and laid beautifully open for inspection by the restless action of the Solway waves. Of the whole shore we made a careful survey. The shore is skirted by a high cliffy bank at various distances from tide-mark, clothed with shrubbery and grass, that once formed the old coast line. Underneath this cliff stretches the rocky shore, washed by the daily tides, exhibiting a belt of Carboniferous strata. The rocks are of different heights, and variously sloped and contorted, always jagged and dark, sometimes rising high and striking, and then sinking under the fine sand of the Firth. The most interesting portion of these rocks lies between Bor- ron Point and the Thirlstone, stretching to equal distances on both sides of the gardener's house of Arbigland, which forms the centre of observation. The limestone is found chiefly between the gardener's house and Borron Point; the coal and iron south of the Thirlstone; the sandstone all along the shore, but best at and near the Thirlstone; the shales everywhere, but more be­ tween the Thirlstone and the Great Boulder, a little south of the gardener's house. South of his house the old coast line becomes the present sea cliff, and has been worn into caves, and hollowed into various picturesque masses by the fierce waves that roll in from the Irish Sea. South of the Thirlstone the rocks leave the beach and run across Gillfoot Bay, which is sandy, but again Downloaded from http://trned.lyellcollection.org/ at Nanyang Technological University on April 26, 2015 280 EDINBURGH GEOLOGICAL SOCIETY. strike the coast at Southerness, where they form the shore, but soon again disappear in the wide waste of the Mersehead Sands. It is this carboniferous shore that exhibits the notable pheno­ mena to which we would now shortly direct your attention, and from which the specimens we exhibit have been brought. The Variety of the Strata.—One of the first features that strikes a visitor is the varied character of the rocks exposed, their sudden transitions, and strange interminglings. Here in a walk of a mile or two we pass over a varied succession of granite, Silurian slate, carboniferous sandstone, shale, limestone, iron­ stone, coal, and trap; while the shore is strewed with boulders (and rocks) of various size, representatives of the inland rocks, brought thither by the glaciers of the past. All these are beau­ tifully exposed and laid open for inspection in successive lines, like as in a great seaside museum, in which a tyro in the science might learn to distinguish the different kinds of rocks. Variations in Dip and Strike, Slip.—Another feature of this shore is the remarkable and sudden variations in the dip and strike of the various rocks that skirt it. It is almost impos­ sible to give any one direction as the general one; but they incline more to run from north-east to south-west than in any other direction that is in the line of the general strike of the Carboniferous belt. But they look towards every point of the compass. North of Borron Point the strike goes variously north­ west ; immediately south of it they sweep round to north-east; towards the gardener's house they turn round again towards the north-west, but some run nearly north and south; south of the house they strike east and west; opposite the garden gate a new series Suddenly interrupts the others, and runs south and east, and this continues unchanged for a considerable distance till south of the Thirlstone the strata abruptly take a north-east direction, only to be again and again interrupted by some new and abrupt strike. The rocks have a tendency to sweep in great circles, as seen at Borron Point, and in both sides of the gardener's house. But at two points the strata take the form of very complete concentric circles. One of these lies a little north of the gardener's house. Unless seen, it could not be thought that such a beautiful cir­ cular section of rocks could be shown in so small a space. The other concentric series is near the Arbigland Boulder, south of the gardener's house; but though evident enough, it is not so remarkable as the other to the north, and cannot be looked down on from above in the same way. The change of dip of the rocks is as varied and sudden as that of the strike. They lie at every angle from horizontal to per­ pendicular; they have even been thrown to a wide angle over the perpendicular. This variation in dip, even in the same seam, is Downloaded from http://trned.lyellcollection.org/ at Nanyang Technological University on April 26, 2015 ON THE GEOLOGY OF SOUTHERNESS. 281 well seen at Borron Point, where one sandstone bed runs very nearly north and south, quite erect and high, like a long black artificial wall. " Troubles" are plentiful, other rocks suddenly appearing in the midst of any one formation, and it is often impossible to say which is the original rock, so numerous and mixed are the seams. Of this a very fine example may be seen near the Great Boulder, where the rock has been thrown in every direction, and is com­ posed of every material in the most incredible manner.

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